Hynobius sengokui, Matsui & Misawa & Yoshikawa & Nishikawa, 2022

Matsui, Masafumi, Misawa, Yasuchika, Yoshikawa, Natsuhiko & Nishikawa, Kanto, 2022, Taxonomic reappraisal of Hynobius tokyoensis, with description of a new species from northeastern Honshu, Japan (Amphibia: Caudata), Zootaxa 5168 (2), pp. 207-221 : 213-217

Hynobius sengokui sp. nov.

Iwaki salamander

[Japanese name: Iwaki-sansyou-uwo]

( Figs. 4 , 5 , 6 )

Hynobius tokyoensis (part): Tago 1931, p. 114.

Hynobius (Hynobius) nebulosus tokyoensis (part): Nakamura & Uéno 1963, p. 7.

Holotype. KUHE 21559 , an adult male from Negoya, Ogawa, Kawabe-machi (36 o 54′N, 140 o 43′E, alt. 27 m above sea level) in Iwaki-shi, Fukushima Prefecture, collected by Y. Misawa on 10 April 1996.

Paratypes. Fukushima Prefecture: Iwaki-shi , KUHE 21560–21567 , 64042–64053 , NSMT-H 12543–12544 , 13420–13422 , 13781 , 17087 . Ibaraki Prefecture: Daigo-machi , NSMT-H 17082 ; Hitachiomiya-shi , NSMT-H 13736–13737 , 17073–17079 ; Kitaibaraki-shi , NSMT-H 11190 , 17083–17084 .

Referred specimens. Fukushima Prefecture: Iwaki-shi, Kawabe-machi KUHE 18393. Ibaraki Prefecture: Hitachiota-shi, KUHE 8099–8118, 8122–8125; Daigo-machi, KUHE 38616, 38617, 43744.

Etymology. The specific name " sengokui " is dedicated to the late Mr. Showichi Sengoku of Japan Wildlife Research Centre who made great contributions to popularize reptiles and amphibians among Japanese.

Diagnosis. Hynobius sengokui sp. nov. is a lentic, but sometimes lotic, breeder, and like the species of the nebulosus group ( Sato 1943) of Hynobius , it has a compressed tail and a large number of small, pigmented, ova per clutch, in contrast to a cylindrical tail and a small number of large, unpigmented ova per clutch in the naevius group ( Sato, 1943). Phylogenetically, H. sengokui sp. nov. forms a mitochondrial DNA clade with H. tokyoensis , which is the sister clade of H. lichenatus in nuclear data, and lacks yellow stripes on edges of the tail. However, H. sengokui sp. nov. lacks striations on the envelope of egg sacs unlike H. lichenatus . Hynobius sengokui sp. nov. is distinguished from H. tokyoensis by its relatively longer axilla-groin distance, shorter trunk, and deeper vomerine teeth series.

Description of holotype (measurements in mm). Head-body moderate (SVL 62.8) and slender; head oval and moderately depressed, distinctly longer (HL 14.9, 23.8%SVL) than wide (HW 10.0, 15.9%); snout rounded, slightly projecting beyond lower jaw; nostril close to snout tip; labial fold absent; eye large, prominently protruded, inset from edge of head in dorsal view; upper eyelid well developed (UEW 1.5, 2.4%SVL), shorter (UEL 4.0, 6.3%SVL) than snout (SL 4.7, 7.4%SVL); gular fold distinct, curving slightly anteriorly; parotoid gland evident, extending from angle of jaw to gular fold; postorbital grooves distinct, branching posterior to angle of jaw, one short and running down to lower jaw, the other long and posteriorly to parotoid gland; vomerine tooth series U-shaped ( Fig. 6 ), wider (VTW 3.6, 5.8%SVL) than long (VTL 2.6, 4.2%SVL), anterior margin at level connecting anterior margins of choana; tongue broad, both sides free from mouth floor; fore- and hindlimbs long and thin (FLL 15.6, 24.9%SVL; HLL 17.9, 28.5%SVL); CGN 12; depressed limbs separated by half a costal fold (LON −0.5); relative length of fingers I <IV <III <II, toes V <I <II <IV <III; fifth toe ill-developed (5TL 1.9, 3.1%); cloaca longitudinal slit; genital tubercle on anterior cloaca present; tail long (TAL 51.8, 82.5%SVL), cylindrical at base (BTAW 8.1, 12.9%SVL; BTAH 6.7, 10.7%SVL) but compressed posteriorly (MTAW 4.2, 6.7%SVL; MTAH 6.9, 11.0%SVL), dorsal fin not evident posteriorly (MXTAH 7.8, 12.4%SVL); tip of tail rounded in lateral view.

Additional Measurements and counts of the holotype: IND (4.0, 6.4%SVL); IOD (3.8, 6.1%SVL); AGD (30.9, 49.3%SVL); TRL (47.8, 76.2%SVL); 2FL (3.2, 5.1%SVL); 3FL (2.8, 4.4%SVL); 3TL (4.9, 7.8%SVL); UJTN (83); LJTN (62); VTN (42).

Color. In life, dorsal side of head, body, and limbs ocher vaguely dotted with dark brown ( Fig. 5A ). Underside pinkish grey without marking, except for throat covered with white nuptial color ( Fig. 5B ). Tail lighter than body without median yellow stripe dorsally and ventrally. In preservative, colors tending to fade but otherwise without obvious change.

Variation. Morphometric data are summarized in Table 2 . The number of costal grooves (CGN) varied from 11 to 12 (median = 12). Adpressed fore- and hindlimbs usually not meeting, except for a few individuals (LON −1.5 to 0.5 with median of −0.5 folds). The northern population from Fukushima tends to be smaller than the southern population from Ibaraki (mean SVL 55.5 mm and 61.0 mm, respectively), and has relatively lower tail. Underside of body sometimes with silvery white flecks, and throat of males in non-breeding season without white nuptial color.

Comparisons. Like the phylogenetically close species H. tokyoensis and H. lichenatus , H. sengokui sp. nov. lacks yellow stripes on edges of the tail, that are present in more western species such as H. vandenburughi and H. nebulosus . Although the variation ranges largely overlap, H. sengokui sp. nov. has relatively longer axilla-groin distance (RAGD = 46.5–55.3% SVL), shorter trunk (RTRL = 73.3–78.4% SVL), and deeper vomerine teeth series (R = 2.9–5.2% SVL) than its sister species H. tokyoensis (43.6–55.0%, 73.4–80.7% and 2.6–4.6% SVL, respectively). The new species with usually separated adpressed limbs can be easily differentiated from the parapatric H. lichenatus with well-overlapping limbs. They are also clearly distinguished by the absence in H. sengokui sp. nov. and presence in H. lichenatus of clear striations on the egg sac envelope.

Mitochondrial differentiation. According to Matsui et al. (2007), means (± SE) of the p-distances in cyt b + control region (808bp) were 4.1 ± 0.4% between H. sengokui sp. nov. and H. tokyoensis , 0.8 ± 0.2% in H. sengokui sp. nov., and 1.0 ± 0.2% in H. tokyoensis among samples. P-distances in cyt b (1141bp), calculated from GenBank data shown in Matsui et al. (2007) were 5.7 ± 0.3% between H. sengokui sp. nov. and H. tokyoensis . Among samples in H. sengokui sp. nov., the distance was 1.1 ± 0.0% as compared with 1.1 ± 0.4% in H. tokyoensis .

Eggs and egg sacs. The egg sacs are crescent or curved banana-like in shape, not coiling, with a thin envelope lacking wrinkles and notable striations. The free ends of egg sacs are slightly elongated tubularly but lacking distinct whiptail structure ( Fig. 7 ). Length of the egg sac ( ESL) ranges from 106–134 (mean ± SD = 119.7 ± 9.1) mm and the width ( ESW) from 15–23 (mean ± SD = 19.6 ± 2.6) mm, with ESL / ESW being 5.0–7.5 (median = 6.0). Clutch size is 32–104 (mean ± SD = 62.6 ± 14.8, n=126). The diameter of ova from five females ranges from 2.5–3.7 (mean ± SD = 3.0 ± 0.2, n = 350) mm. The animal pole is dark gray and vegetal pole is light gray in color .

Range. Narrow ranges of the southeastern Tohoku and northeastern Kanto regions of eastern Honshu. Known only from southeastern Fukushima, southeastern Tochigi, and northern Ibaraki prefectures. Known localities range from 11 m to 321 m above sea level ( Fig. 8 ) .

Natural history. Inhabits in and around forests. The breeding season is from March to April. Breeding normally takes place in still-waters of springs, pools, and paddies, but sometimes in slowly flowing waters. Egg sacs are laid under stones or attached to water plants in the water.

Protection. Under the name of H. tokyoensis , the new species has been listed as vulnerable on the IUCN Red List ( Matsui et al. 2021: status VU) and Japanese Red List (2020: VU). It is also listed on the Prefectural Red List of Fukushima, 2020 (EN), and Ibaraki, 2016 (NT), and protected by each local government.

Figures

FIGURE 4. Alive male of Hynobius sengokui sp. nov. from Iwaki-shi (not captured).

FIGURE 5. Dorsal (A) and ventral (B) views of male paratype (NSMT-H 17087) of Hynobius sengokui sp. nov. from Iwaki-shi. Scale bar shows 20 mm.

FIGURE 6. Open mouth of holotype (KUHE 21559) of Hynobius sengokui sp. nov. from Iwaki-shi, showing the shape of vomerine tooth series. Scale bar indicates 1 mm.

FIGURE 7. Egg sac of Hynobius sengokui sp. nov. from Hitachiomiya-shi. Scale bar indicates 20 mm.

FIGURE 8. Map of southern Tohoku and Kanto, Japan, showing the distribution ranges and type localities of Hynobius sengokui sp. nov. (hatched, closed circle) and H. tokyoensis (grey, open circle). For the number of the sampling localities (closed squares), refer to Table 1.